Fish Oil

What is it?

Fish oil can be obtained from eating fish or by taking supplements. Fish that are especially rich in the beneficial oils known as omega-3 fatty acids include mackerel, herring, tuna, salmon, cod liver, whale blubber, and seal blubber. Two of the most important omega-3 fatty acids contained in fish oil are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Make sure to see separate listings on EPA and DHA, as well as Cod Liver Oil, and Shark Liver Oil.

Fish oil is FDA approved to lower triglycerides levels, but it is also used for many other conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure, triglycerides and cholesterol levels. Fish oil has also been used for preventing heart disease or stroke, as well as for clogged arteries, chest pain, irregular heartbeat, bypass surgery, heart failure, rapid heartbeat, preventing blood clots, and high blood pressure after a heart transplant.

Fish oil is also used to for many kidney-related problems including kidney disease, kidney failure, and kidney complications related to diabetes, cirrhosis, Berger's disease (IgA nephropathy), heart transplantation, or using the drug called cyclosporine.

Women sometimes take fish oil to prevent painful periods; breast pain; and complications associated with pregnancy such as miscarriage (including that caused by a condition called antiphospholipid syndrome), high blood pressure late in pregnancy, early delivery, slow infant growth, and to promote infant development.

Fish oil is also taken by mouth for weight loss, exercise performance and muscle strength, muscle soreness after exercise, pneumonia, cancer, lung disease, seasonal allergies, chronic fatigue syndrome, and for preventing blood vessels from re-narrowing after surgery to widen them.

Effective for...

High triglycerides. Research suggests that fish oil from supplements and food sources can reduce triglyceride levels. The effects of fish oil appear to be the greatest in people who have very high triglyceride levels. Also the amount of fish oil consumed seems to directly affect how much triglyceride levels are reduced. One particular fish oil supplement called Lovaza has been approved by the FDA to lower triglycerides. A one-gram capsule of Lovaza contains 465 milligrams of EPA and 375 milligrams of DHA. But, a small study suggests that taking fish oil daily for 8 weeks might not reduce triglycerides in adolescents.

Likely Effective for...

Heart disease. Research suggests that eating fish can be effective for keeping people with healthy hearts free of heart disease. People who already have heart disease might also be able to lower their risk of dying from heart disease by eating fish. The picture is less clear for fish oil supplements. For people who already take heart medications such as a "statin" and those who already eat a decent amount of fish, adding on fish oil might not offer any additional benefit.

Possibly Effective for...

Preventing re-blockage of blood vessels after angioplasty, a procedure to open a closed blood vessel. Research suggests that fish oil decreases the rate of blood vessel re-blockage by up to 45% when given for at least 3 weeks before an angioplasty and continued for one month thereafter. But, when given for 2 weeks or less before angioplasty, it doesn't seem to have any effect.

Miscarriage in pregnant women with an autoimmune disorder called antiphospholipid syndrome. Taking fish oil by mouth seems to prevent miscarriages and increase live birth rates in pregnant women with antiphospholipid syndrome.

Attention deficit-hyperactivity disorder (ADHD) in children. Early research shows that taking fish oil improves attention, mental function, and behavior in children 8-13 years-old with ADHD. Other research shows that taking a specific supplement containing fish oil and evening primrose oil (Eye Q, Novasel) improves mental function and behavior in children 7-12 years-old with ADHD.

Bipolar disorder. Taking fish oil along with conventional treatments for bipolar disorder seems to improve symptoms of depression but not mania in people with bipolar disorder.

Cancer-related weight loss. Taking a high dose of fish oil seems to slow weight loss in some cancer patients. Low doses of fish oil don't seem to have this effect. Some researchers believe fish oil slows cancer-related weight loss by fighting depression and improving the mood of people with cancer.

Dry eye. Some clinical research shows that eating more fish oil is linked to a lower risk of getting dry eye syndrome in women. Other research shows that taking a specific fish oil product (PRN Dry Eye Omega Benefits softgels) daily modestly improves symptoms of dry eye such as pain, blurred vision, and sensitivity. Other research using other forms of fish oil products suggests that taking these supplements for 4-12 weeks modest improves some dry eye symptoms. However, the sensation of eye dryness is not always improved. Other research also shows that taking a specific combination products containing fish oil and other ingredients might improve some dry eye symptoms; however, this research is conflicted and poor quality.

High blood pressure caused by the drug cyclosporine. Cyclosporine is a medication that reduces the chance of organ rejection after an organ transplant. Taking fish oil seems to prevent high blood pressure caused by this drug.

Damage to the kidneys caused the drug cyclosporine. Cyclosporine is a medication that reduces the chance of organ rejection after an organ transplant. Taking fish oil seems to prevent kidney damage in people taking this drug. Fish oil also seems to improve kidney function during the recovery phase following the rejection of a transplanted organ in people taking cyclosporine.

Developmental coordination disorder (DCD). A combination of fish oil (80%) and evening primrose oil (20%) seems to improve reading, spelling, and behavior when given to children age 5-12 years with developmental coordination disorder. However, it does not seem to improve motor skills.

Menstrual pain (dysmenorrhea). Research shows that taking fish oil, alone or with vitamin B12, can improve painful periods and reduce the need for pain medications in women with menstrual pain.

Movement disorder in children (dyspraxia). Taking a fish oil product that also contains evening primrose oil, thyme oil, and vitamin E (Efalex, Efamol Ltd) seems to decrease movement disorders in children with dyspraxia.

Endometrial cancer. There is some evidence that women who regularly eat about two servings of fatty fish weekly have a reduced risk of developing endometrial cancer.

Heart failure. Research shows that a higher intake of fish oil from foods or supplements is linked with a reduced risk for heart failure.

Abnormal cholesterol caused by HIV/AIDS treatment. Some research suggests that taking fish oil reduces triglyceride levels in people with abnormal cholesterol levels caused by HIV/AIDS treatment. Taking fish oil might also reduce total cholesterol levels in these people, although results are inconsistent.

High blood pressure. Fish oil seems to slightly lower blood pressure in people with moderate to very high blood pressure. Some types of fish oil might also reduce blood pressure in people with slightly high blood pressure, but results are inconsistent. Fish oil seems to add to the effects of some, but not all, blood pressure-lowering medications. However, it doesn't seem to reduce blood pressure in people with uncontrolled blood pressure who are already taking blood pressure-lowering medications.

A certain kidney disease called IgA nephropathy. Some research shows that long-term but not short-term use of fish oil can slow the loss of kidney function in high-risk patients with IgA nephropathy. Fish oil might have greater effects when taken at higher doses. Also, it might be most effective in people with IgA nephropathy who have higher levels of protein in the urine.

Weak bones (osteoporosis). Research suggests that taking fish oil alone or together with calcium and evening primrose oil slows the rate of bone loss and increases bone density at the thigh bone (femur) and spine in elderly people with osteoporosis.

Psoriasis. There is some evidence that administering fish oil intravenously (by IV) can decrease the severity of psoriasis symptoms. Also, applying fish oil to the skin also seems to improve some symptoms of psoriasis. But taking fish oil by mouth does not seem to have any effect on psoriasis.

Psychosis. Some research shows that taking a fish oil supplement might help prevent full psychotic illness from developing in teenagers and young adults with mild symptoms. These effects of fish oil have not been tested in older people.

Raynaud's syndrome. There is some evidence that taking fish oil can improve cold tolerance in some people with the usual form of Raynaud's syndrome. However, people with Raynaud's syndrome caused by a condition called progressive systemic sclerosis do not seem to benefit from fish oil supplements.

Abnormal cholesterol following a kidney transplant. Early research suggests that taking fish oil alone or together with cholesterol-lowering drugs can improve cholesterol levels in people with abnormal cholesterol levels after a kidney transplant.

Rheumatoid arthritis (RA). Taking fish oil by mouth, alone or together with the drug naproxen (Naprosyn), seems to help improve symptoms of RA. People who take fish oil can sometimes reduce their use of pain medications. Also, administering fish oil intravenously (by IV) reduces swollen and tender joints in people with RA.

Stroke. Moderate fish consumption (once or twice weekly) seems to lower the risk of having a stroke by as much as 27%. However, very high fish consumption (more than 46 grams of fish per day) seems to increase stroke risk, perhaps even double it. Eating fish does not lower stroke risk in people who are already taking aspirin for prevention.

Possibly Ineffective for...

Chest pain (angina). Research suggests that taking fish oil supplements does not reduce the risk of death or improve heart health in people with chest pain. Some evidence even suggests that fish oil supplements might actually increase the risk of heart-related death in people with chest pain.

Hardening of the arteries (atherosclerosis). Some research shows that taking fish oil supplements might slightly reduce the progression of atherosclerosis. But most research shows that fish oil doesn't slow the progression or improve symptoms of atherosclerosis.

Irregular heartbeat (atrial fibrillation). Some research suggests that people who eat fish five or more times weekly have a reduced risk of irregular heartbeat. But most research suggests that eating fatty fish or taking fish oil supplements does not reduce the risk of irregular heartbeat.

Brain disorder due to blood blow problems (cerebrovascular disease). Some early research suggests that eating fish reduces the risk of cerebrovascular disease. But higher quality research suggests that taking fish oil does not have this effect.

Leg pain due to blood flow problems (claudication). Taking fish oil by mouth does not appear to improve walking distance in people with leg pain due to blow flow problems.

Mental function. Some early research suggests that eating fish or consuming higher amounts of fish oil from dietary sources is linked to improved mental function and reduced mental decline in older people. But, most evidence shows no benefit on mental function in older people or young adults and children.

Pneumonia. Population research shows no relationship between fish consumption and the risk of developing pneumonia.

Blood infection (sepsis). Research suggests that administering fish oil intravenously (by IV) does not improve survival or reduce brain injury in people with sepsis.

Abnormal rapid heart rhythms (ventricular arrhythmias). Population research suggests that eating a lot of fish has no effect on the risk for abnormal rapid heart rhythms. Clinical research is inconsistent. Some research shows that taking fish oil daily does not affect the risk for abnormal heart rhythms. But other research shows that taking fish oil for 11 months delays the development of the condition. However, overall, taking fish oil does not seem to reduce the risk of death in people with abnormal rapid heart rhythms.

Likely Ineffective for...

Diabetes. Taking fish oil does not lower blood sugar in people with type 2 diabetes. However, fish oil can provide some other benefits for people with diabetes, such as lowering blood fats called triglycerides.

Insufficient Evidence to Rate Effectiveness for...

Age-related vision loss. There is some evidence that people who eat fish more than once weekly have a reduced risk of developing age-related vision loss. But, clinical research shows that taking fish oil by mouth for up to 5 years does not prevent vision loss.

Seasonal allergies (hayfever). Early research suggests that mothers who take fish oil supplements during the late stages of pregnancy may lower the occurrence of allergies in their children. But other research suggests that fish oil does not reduce the development of allergies in children when taken by the mother during pregnancy.

Alzheimer's disease. There is some early evidence that fish oil might help prevent Alzheimer's disease. However, it does not seem to help prevent a decline in thinking skills for most people who have already been diagnosed with Alzheimer's disease.

Asthma. Some research suggests that fish oil supplements might help TREAT some asthma symptoms, but results are not consistent. Some research shows that taking fish oil improves breathing and reduces the need for medication, but other research suggests that fish oil does not reduce the severity of asthma is children.

It is also not clear if fish oil can help PREVENT asthma. Some early research suggests that mothers who take fish oil supplements daily during pregnancy reduce the risk of asthma in their children by 35% to 63%. But, fish oil does not seem to provide any benefits when taken while breastfeeding.

Scaly, itchy skin (eczema). Fish oil might help PREVENT eczema, but research is not consistent. Some early research suggests that mothers who take fish oil supplements during pregnancy reduce the risk of severe eczema in their infants. Also, population research suggests that children who eat fish at least once weekly from 1 to 2 years of age have a lower risk of developing eczema. But other research, including recent studies, suggests that neither supplementation during pregnancy nor supplementation during infancy reduces the risk of eczema. Overall, research suggests that fish oil does not help TREAT eczema once it has developed.

Autism. Some early research suggests that taking fish oil might lower hyperactivity in children with autism. Other research suggests it does not.

Cancer. Research on the effects of fish oil in preventing cancer has produced conflicting results. Some population research suggests that eating fish or having higher blood levels of omega-3 fatty acids from fish oil is linked to a lower risk of different cancers, including oral cancer, pharyngeal cancer, esophageal cancer, colon cancer, rectal cancer, breast cancer, ovarian cancer, and prostate cancer. But other research suggests that eating fish does not reduce the risk of cancer.

Cataracts. There is some early evidence that eating fish three times weekly can slightly lower the risk of developing cataracts.

Chronic fatigue syndrome (CFS). There is some conflicting evidence about the use of a specific product (Efamol Marine) that combines fish oil and evening primrose oil to reduce the symptoms CFS.

Chronic kidney disease. Early evidence shows that fish oil might benefit some people with chronic kidney disease who are receiving dialysis treatments. But it's not clear if fish oil helps people with poor kidney function who are otherwise healthy.

Abnormal cholesterol caused by clozapine. Clozapine is a drug used to treat schizophrenia. Early evidence suggests that taking fish oil reduces triglyceride levels, but increases total cholesterol and low-density lipoprotein (LDL or "bad") cholesterol, in people with abnormal cholesterol levels due to taking clozapine.

Colorectal cancer. Some early research suggests that taking fish oil during chemotherapy might slow the progression of tumors in people with colorectal cancer.

Crohn's disease. Research into the effects of fish oil on Crohn's disease has produced conflicting results. Some research shows that taking a specific fish oil product (Purepa, Tillotts Pharma) can reduce the relapse of Crohn's disease for people who have recovered. However, other research shows that fish oil does not have this effect.

Cystic fibrosis. Early research suggests that taking fish oil by mouth can improve lung function in people with cystic fibrosis. However, administering fish oil intravenously (IV) does not have this effect.

Memory loss (dementia). Some early research suggests that eating fish at least once per week reduces the risk of developing dementia. Other research suggests there is no link between fish consumption and the risk of dementia.

Depression. There is inconsistent evidence on the effect of taking fish oil for depression. Some research shows that taking fish oil along with an antidepressant might help improve symptoms in some people. Other research shows that taking fish oil does not improve depression symptoms. The conflicting results may be due to the amount of EPA and DHA in the supplement or the severity of depression before treatment.

Kidney damage in people with diabetes (diabetic nephropathy). Evidence suggests that taking fish oil does not improve kidney function in people with diabetic nephropathy.

Dyslexia. Taking fish oil by mouth seems to improve night vision in children with dyslexia.

Abnormal cholesterol or fat levels in the blood (dyslipidemia). There is conflicting evidence about the effects of fish oil on cholesterol and fat levels in the blood. Some research shows that taking fish oil can lower triglyceride levels, low density lipoprotein (LDL or "bad") cholesterol, and increase high density lipoprotein (HDL or "good") cholesterol in people with abnormal cholesterol levels. However, other research shows that taking fish oil daily does not have this effect.

Epilepsy. Research suggests that taking omega-3 fatty acids from fish oil by mouth daily for 10 weeks reduces seizures in people with epilepsy that is resistant to drugs.

Muscle soreness due to exercise. Some research shows that taking fish oil by mouth daily for 1-6 months before and during exercise does not prevent muscle soreness in the elbow or the knee when contracted. But other research suggests that taking fish oil improves soreness from knee extension exercises.

Exercise performance. Some evidence suggests that taking fish oil can improve lung function in athletes. But other evidence suggests that taking fish oil does not improve endurance, recovery, heart rate, or exercise duration.

Preventing blockage of grafts used in kidney dialysis. Taking higher doses of fish oil short-term seems to help prevent blood clot formation in hemodialysis grafts. Taking lower doses long-term does not seem to have this effect.

Prediabetes. Early studies suggest that fish oil may help prevent prediabetes from advancing to type 2 diabetes.

Infant development. There is some evidence that mothers who eat fish or take fish oil supplements during pregnancy may improve some aspects of their baby's mental development. Taking fish oil during breast-feeding does not have this effect. However, feeding infants formula fortified with fish oil appears to improve some aspect of the baby's vision by the age of 2 months.

Multiple sclerosis. Taking a specific fish oil product (MaxEPA) does not appear to improve the duration, frequency, or severity of relapses in patients with multiple sclerosis.

Muscle strength. Some research suggests that taking fish oil daily for 90 to 150 days in addition to 90 days of resistance strength training might improve muscle growth and strength in healthy older women.

Weight loss. Some research shows that eating fish improves weight loss and decreases blood sugar in people who are overweight with high blood pressure. Early research also shows that taking a specific fish oil supplement (Hi-DHA, NuMega) lowers body fat when combined with exercise. But other evidence suggests that taking another specific fish oil supplement (Lovaza) does not lower body weight in overweight people.

Swelling of the pancreas (pancreatitis). Evidence suggests that feeding intravenously (IV) with nutrition that has been fortified with fish oil reduces the number of days of kidney replacement therapy needed by people with severe inflammation of the pancreas.

Phenylketonuria (PKU). Some evidence suggests that taking fish oil supplements improves motor skills, coordination, and vision in children with a rare genetic disorder called phenylketonuria.

Post-traumatic stress disorder (PTSD). Some early research shows that adding supplements containing omega-3 fatty acids from fish oil to psychoeducation does not provide any further benefits to people with PTSD.

Pregnancy complications. There is some evidence that taking fish oil or eating seafood during pregnancy can help prevent premature delivery. However, fish oil does not seem to help prevent high blood pressure during pregnancy.

Prematurity. Baby formula that has been fortified with fatty acids from fish oil and borage oil seems to improve growth and nervous system development in premature infants, especially boys.

Bed sores (pressure ulcers). Early research suggests that supplementing either a feeding tube or IV with fish oil for 28 days might slow the progression of pressure ulcers.

Salicylate intolerance. Some early research suggests that taking fish oil might improve symptoms of salicylate intolerance, such as asthma attacks and itching.

Schizophrenia. There is one report of fish oil improving symptoms of schizophrenia in a pregnant woman.

Sickle cell disease. Early research suggests that taking fish oil can reduce severe pain episodes in people with sickle cell disease.

Systemic lupus erythematosus (SLE). Some early studies suggest that fish oil helps improve symptoms of SLE, while other studies show no effect.

Inflammatory bowel disease (ulcerative colitis). Research studies into the effects of fish oil for treating ulcerative colitis show conflicting results.

A lot of the benefit of fish oil seems to come from the omega-3 fatty acids that it contains. Interestingly, the body does not produce its own omega-3 fatty acids. Nor can the body make omega-3 fatty acids from omega-6 fatty acids, which are common in the Western diet. A lot of research has been done on EPA and DHA, two types of omega-3 acids that are often included in fish oil supplements.

Omega-3 fatty acids reduce pain and swelling. This may explain why fish oil is likely effective for psoriasis and dry eyes. These fatty acids also prevent the blood from clotting easily. This might explain why fish oil is helpful for some heart conditions.

Fish oil is LIKELY SAFE for most people when taken by mouth in low doses (3 grams or less per day). There are some safety concerns when fish oil is taken in high doses. Taking more than 3 grams per day might keep blood from clotting and can increase the chance of bleeding.

High doses of fish oil might also reduce the immune system's activity, reducing the body's ability to fight infection. This is a special concern for people taking medications to reduce their immune system's activity (organ transplant patients, for example) and the elderly.

Only take high doses of fish oil while under medical supervision.

Fish oil can cause side effects including belching, bad breath, heartburn, nausea, loose stools, rash, and nosebleeds. Taking fish oil supplements with meals or freezing them can often decrease these side effects.

Fish oil is POSSIBLY SAFE when injected intravenously (by IV) in the short-term. Fish oil or omega-3 fatty acid solutions have been safely used for 1 to 4 weeks.

Consuming large amounts of fish oil from some DIETARY sources is POSSIBLY UNSAFE. Some fish meats (especially shark, king mackerel, and farm-raised salmon) can be contaminated with mercury and other industrial and environmental chemicals. Fish oil supplements typically do not contain these contaminants.

Special Precautions & Warnings:

Children: Fish oil is POSSIBLY SAFE when taken by mouth appropriately. Fish oil has been used safely through feeding tubes in infants for up to 9 months. But young children should not eat more than two ounces of fish per week. Fish oil is POSSIBLY UNSAFE when consumed from dietary sources in large amounts. Fatty fish contain toxins such as mercury. Eating contaminated fish frequently can cause brain damage, mental retardation, blindness and seizures in children.

Pregnancy and breast-feeding: Fish oil is LIKELY SAFE when taken by mouth appropriately. Taking fish oil during pregnancy does not seem to affect the fetus or baby while breast-feeding. Women who are pregnant or who may become pregnant, and nursing mothers should avoid shark, swordfish, king mackerel, and tilefish (also called golden bass or golden snapper), as these may contain high levels of mercury. Limit consumption of other fish to 12 ounces/week (about 3 to 4 servings/week). Fish oil is POSSIBLY UNSAFE when dietary sources are consumed in large amounts. Fatty fish contain toxins such as mercury.

Bipolar disorder: Taking fish oil might increase some of the symptoms of this condition.

Liver disease: Fish oil might increase the risk of bleeding in people with liver scarring due to liver disease.

Depression: Taking fish oil might increase some of the symptoms of this condition.

Diabetes: There is some concern that taking high doses of fish oil might make the control of blood sugar more difficult.

Familial adenomatous polyposis: There is some concern that fish oil might further increase the risk of getting cancer in people with this condition.

High blood pressure: Fish oil can lower blood pressure and might cause blood pressure to drop too low in people who are being treated with blood pressure-lowering medications.

HIV/AIDS and other conditions in which the immune system response is lowered: Higher doses of fish oil can lower the body's immune system response. This could be a problem for people whose immune system is already weak.

An implanted defibrillator (a surgically placed device to prevent irregular heartbeat): Some, but not all, research suggests that fish oil might increase the risk of irregular heartbeat in patients with an implanted defibrillator. Stay on the safe side by avoiding fish oil supplements.

Fish or seafood allergy: Some people who are allergic to seafood such as fish might also be allergic to fish oil supplements. There is no reliable information showing how likely people with seafood allergy are to have an allergic reaction to fish oil. Until more is known, advise patients allergic to seafood to avoid or use fish oil supplements cautiously.

Medications for cancer (Chemotherapy)

Some fish oil products contain small amounts of a fatty acid that is believed to stop certain chemotherapy drugs from working. However, the amount of this fatty acid in most fish oil products is probably too low to be a concern. Until more is known, you do not need to stop taking fish oil if you are also taking medications for cancer.

Using fish oil with medications that slow clotting may increase the risk of bleeding. However, conflicting data exists. Until more is known, use cautiously in combination with medications that slow blood clotting.

Warfarin (Coumadin)

Warfarin (Coumadin) is used to slow blood clotting. Fish oil also might slow blood clotting. Taking fish oil with warfarin might slow blood clotting too much and increase the risk of bleeding. However, conflicting results suggests that fish oil does not increase the effects of warfarin. Until more is known, use cautiously in combination with warfarin. Have your blood checked regularly, as your dose of warfarin (Coumadin) might need to be changed.

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